Results 161 to 170 of about 9,318 (208)

Linear 13C-H coupling constant-Hammett sigma-constant relations in substituted benzaldehydes

Journal of Chemical & Engineering Data, 1972
benzaldehydes, measuring the CI3 -H coupling constant of the aldehydic proton. As expected, the greater ability of the trigonal carbon atom to transmit the electronic effects of substituent X to this proton is reflected in the much greater sensitivity of the Cl3-H coupling constant to the electronic nature of X. Again excellent linear J-a relationships
Claude H. Yoder, Charles D. Schaeffer, Ronald E. Hess   +2 more
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A theoretical treatment of Hammett's sigma constants

Recueil des Travaux Chimiques des Pays-Bas, 1953
AbstractA theoretical treatment is given of the connection between the structure and the position of a substituent S and the value of σs, from the Hammett equation: log ks/ko = ρ · σs. The theory is based on a wave mechanical calculation of the effect of S on the localisation energy of a reaction. The equations derived make it possible to calculate σs,
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Constant no more: reevaluating Hammett constants through spin-crossover

Inorganic Chemistry Frontiers
The spin-crossover phenomenon helped re-evaluate the existing Hammett constants that incorrectly classify electron-withdrawing and electron-donating groups to explain and predict magnetic behaviours, chemical reactivity and beyond.
Igor Nikovskiy, Dmitry Aleshin, Aleksei Anisimov, Valentin Novikov, Yulia Nelyubina   +4 more
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Designing Acid Acid Co-Crystals−The Use of Hammett Substitution Constants

Crystal Growth & Design, 2009
Construction of defined supramolecular synthons is a key aim of crystal engineering. This work reports the use of Hammett substitution constants as a tool in the design of acid-acid cocrystals with a desired R2 2(8) hydrogen-bonded heterodimer. © 2009 American Chemical Society.
Chadwick, Keith, Sadiq, Ghazala, Davey, Roger J., Seaton, Colin C., Pritchard, Robin G., Parkin, Andrew   +5 more
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Hammett constants of the pyrroline-2, 5-dione ring

Chemistry of Heterocyclic Compounds, 1976
The electronic effect of the pyrroline-2,5-dione ring on the benzene ring in the case of N-aryl compounds is close to the effect exerted by halogens. The overall electron-acceptor effect depends markedly on the nature of the solvent. The electron-donor effect of conjugation is small.
V. D. Romanenko, N. N. Kalibabchuk, A. A. Rositskii, V. G. Zalesskaya, V. E. Didkovskii, S. V. Iksanova   +5 more
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Do Hammett constants model electronic properties in QSARs?

Science of The Total Environment, 1991
Abstract A set of 22 alkylated or halogenated phenols was subjected to a comparative analysis of the solution acidity as expressed by p K a , the respective σ Hammett substituent constants and the gas-phase acidity. Quantum chemical calculations within the PM3 model lead to the anion ionization potential as an intrinsic acidity scale for the phenols,
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Correlation between Hammett Substituent Constants and Directly Calculated π-Conjugation Strength

The Journal of Organic Chemistry, 2006
The results of an energy decomposition analysis of ortho-, meta-, and para-substituted benzylic cations and para-substituted benzylic anions H2C-C6H4Rq (R = H, F, CN, Me, OH, NH2, NO2, CHO, CO2H; q = +, -) are presented and discussed. The calculated values for the pi bonding between CH2(q) and C6H4R show for substituents which have pi orbitals a linear
Israel, Fernández, Gernot, Frenking
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Quantum chemical topology (QCT) descriptors as substitutes for appropriate Hammett constants

Organic & Biomolecular Chemistry, 2005
A technique called quantum topological molecular similarity (QTMS) was recently proposed [J. Chem. Inf. Comput. Sci., 2001, 41, 764] in order to construct a variety of medicinal, ecological and physical organic QSAR/QSPRs, based on modern ab initio wave functions of geometry optimised molecules, in combination with quantum chemical topology (QCT).
Smith, P. J., Popelier, P. L A
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Structure—property relationships and momentum space quantities: Hammett σ—constants

Molecular Physics, 2003
Correlations are established between Hammett σ constants and momentum-space expectation values ( ). Momentum-space quantities, which have generally been neglected by chemists, are shown to be valuable for such problems, which suggests they may be useful more widely as suitable molecular descriptors for quantitative structure-property studies.
LLUÍS AMAT, RAMON CARBÓ-DORCA, DAVID L. COOPER, NEIL L. ALLAN, ROBERT PONEC   +4 more
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Hammett-Taft constants of substituted 2- and 4-quinazolinyl groups

Bulletin of the Academy of Sciences of the USSR Division of Chemical Science, 1991
From the chemical shifts of the meta- and para-carbon atoms of the phenyl group in phenylquinazolines the σI and σR0 constants of 2- and 4-quinazolinyl groups were determined. Correlation equations which enable us to calculate the σ constants of various substituted 2- and 4-quinazolinyl groups are proposed.
S. G. Baram, O. P. Shkurko, V. P. Mamaev
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